The invention relates to a combination-paper machine, especially to one adapted for the continuous manufacture of thick paper, cardboard or the like, having two perforated cylinders with a web-combining point between them, and devices for feeding the pulp suspension onto the perforated cylinders prior to the combining point, whereby an endless wire is guided along at least that surface of each perforated cylinder which is between the pulp suspension feeding point and the combining point.
Previously known is a combination-paper machine for the continuous manufacture of thick paper in layers, having several successive cylinder units at a certain interval from each other, below which there is fitted an endless lower wire or felt common to all the units to receive and combine the paper webs. The cylinder units also share a common felt or wire which runs over part of their surface and which has been fitted to run alternately against the surface of each cylinder unit from the first to the last, and from there back to the first cylinder unit with the purpose of transferring the pulp web formed on each cylinder to the lower wire in order to combine the webs.
With this previously known combination-paper machine, the water can be extracted from each layer separately and on both sides. Thereby the wet limit of each layer is reached even before the layers are combined, which results in the disadvantage that the adhesion of the layers to each other may be poor.
In addition, through U.S. Pat. No. 2,911,039 a paper machine is known which has two perforated cylinders which have been fitted one on top of the other so that a pressing point is formed between them. Two wires are guided through this point and each of them has been fitted to run along part of the surface of its own cylinder prior to the pressing point. On this surface part, pulp suspension is fed onto each wire separately from two feeding boxes operated by pressure, each feeding box having a curved lip extending over the said part of the cylinder and the feeding boxes together with the cylinders and the pressing point forming a closed space which is under pressure. The pressing space is approximately equal to the thickness of the completed web, so that substantially all the water is extracted before the pressing point. Thus the water is extracted from each layer on one side through the cylinder surface part under the curved lip.
Even this apparatus has a disadvantage in that the wet limit is reached before the layers meet since almost all the water is extracted before the pressing point. Between the meeting point of the feeding-box upper lips and the pressing point the layers are, it is true, in contact with each other over a very short distance, but in this area the webs no longer contain very much water as it is necessary to extract the water from each layer separately long before the pressing point in the space between the curved lip and the cylinder. Even this distance would be too short if pressure were not used as an aid to make the extraction of water more effective.
Some of the disadvantages of this apparatus are thus the extraction of water on one side only, the fact that the layers are combined substantially only after their reaching the wet limit, at which time the layers adhere poorly to each other, the fact that the extraction of water is carried out over too short a distance, which may result in an uneven distribution of the fibers in the web, and that sealing between the pressure feeding boxes and the perforated cylinders is difficult when the feeding boxes are under high pressure.
The object of the present invention is to eliminate the above disadvantages.